1. Field of the Invention
The present invention is related to a dual- or multi-frequency planar F-antenna, and especially to a planar antenna suitable for installing in different interior spaces on various equipment of dual- or multi-frequencies.
2. Description of the Prior Art
A spiral coil which is wound by metal wires is of the major type of antenna. Any of the followings including the diameter or the material of a coil or the pitch between rings of a coil or the total length of a coil of this kind of helix antenna will affect the set function. But the defect of such conventional helix antenna resides in three-dimensional protruding out of the equipment. As for communication equipment of the modern miniaturized type or with necessary built-in antennas (such as a mobile phone or a portable computer), it can hardly be surely desirable.
Thus, various miniaturized and planar microstrip antennas were gradually researched and developed. But in the early time, microstrip antennas such as those disclosed in U.S. Pat. Nos. 3,921,177 and 3,810,183 usually consisted of round or rectangular thin metal sheets. Dielectric substance is filled between the antenna and the ground. Generally speaking, this kind of microstrip antenna can go compatible only with narrower bandwidths. However, U.S. Pat. Ser. No. 07/695,686, abandoned, provides a polygonal spiral-type microstrip antenna which is an improvement on the early microstrip antennas; its bandwidth is close to that of a general helix antenna of constant impedance. But the defect of this kind of microstrip antenna is that, for low frequencies, the diameter of the antenna becomes quite large and is not suitable for modern portable communication equipment.
Among the modern applicable embodiments of the planar antennas, the relatively more notable one is the kind of planar inverted F-antenna (PIFA). The structure of such a planar inverted F-antenna, as shown in FIG. 1, comprises a metal wire 11 provided on a grounding surface 10, a short point 12 is provided on one end of the metal wire 11 and a feed point 13 is provided near the short point 12, the feed point 13 is connected to a feed-in axle 14. In this way, a desired single-frequency antenna is formed. This early type of inverted F-antenna can be developed to get a planar inverted F-antenna as shown in FIG. 2. Basically it includes a metal surface 15 of a predetermined area, and other related items including a grounding surface 100, a short point 120, a feed point 130 and a feed-in axle 140.
It was stated in xe2x80x9cDual-Frequency PIFAxe2x80x9d on page 1451 of xe2x80x9cIEEExe2x80x9d published in October of 1997 that, either to merge two separate blocks of different sizes into a rectangular shape or to provide an open slot with two mutually perpendicular sections on a rectangular metal surface can form a desired dual frequency PIFA. But the problem is that different mode mobile phones of different brands include slightly different operating frequencies and various interior installation spaces for antennas. Obviously, the art supplied in the abovementioned document is unable to solve thoroughly the problem of installing these dual- or multi-frequency PIFA in mobile phones of different brands.
The object of the present invention is to provide a dual- or multi-frequency PIFA; the device can match various interior installation spaces of communication equipment, and becomes a proper built-in planar dual- or multi-frequency PIFA.
To achieve the object, the metal surface on the top of the grounding surface of this invention is partitioned into a long and a short section of different sizes by a deformed and curved open slot, of which the short point and the feed point can be adjusted properly. The length from the short point to the end point of the short section and the length on the long section from the short point to the open end of the open slot are decided by the resonance frequencies of themselves.
The present invention will be apparent in its novelty and other features after reading the detailed description of the preferred embodiment thereof in reference to the accompanying drawings.